It did pinch down. He went back into the face cut and did some trimming at about 3:08 in the vid. Then at about 3:28 you can hear the saw pinched as it swings through aways.
The axe in the back cut to me serves two purposes, one it does give you a visual to see the opening or closing of the kerf. Two if it does set back your kerf is still open to get a wedge into. With the axe having a handle they will come out easier if stuck.
The guy does a good job. But not something for your average Joe too try.
Some times they work, other times you walk down the block to get another saw to cut you out.
B, I will re watch his back slip vid. I think I know how he did it.